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Why Do We Ever Stop Eating? Taste, Reward, and Hyperpalatability (Why Are We Hungry? Part VII)

Caution: contains SCIENCE!

In this article, I begin assembling several of the concepts from previous articles. I’ve linked to them whenever possible—but if you find yourself confused by concepts or terminology, you might find it worthwhile to re-read the series starting from Part I.

(This is part VII of a series. Go back to Part I, Part II, Part III, Part IV, Part V, or Part VI.)

Summary: Our Story Thus Far

In previous installments, we’ve established the following:

  • Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.
  • In a properly functioning human animal, likes and wants coincide; satiation is an accurate predictor of satiety; and the combination of hunger signals (likes and wants) and satisfaction signals (satiation and satiety) results in energy and nutrient balance at a healthy weight and body composition.
  • Restrained eating requires the exercise of willpower to override likes, wants, and the lack of satiation or satiety; the exercise of willpower uses energy and causes stress; and stress makes you eat more. Therefore, a successful diet must minimize the role of willpower.
  • A lack of satiety will leave us hungry no matter what else we do to compensate. We fail to achieve satiety by not ingesting (or not absorbing) the energy and/or nutrients our body requires, and by an inability to retrieve the energy and/or nutrients our bodies have stored due to mitochondrial dysfunction.
  • Satiation is an estimate of future satiety based on sensory input. As with satiety, we fail to achieve it by not satisfying our nutritional needs. We can also bypass satiation by decreasing sensory exposure to our foods. Some common enablers are eating quickly, eating while distracted or on the run, and eating calorie-dense packaged and prepared foods.
  • The role of reward in hunger constitutes hedonic impact (“liking”, palatability) and incentive salience (“wanting”, the drive to consume more food). The process of learning modifies both. Furthermore, reward is not limited to food, is neither static nor an intrinsic property of the food itself, and is modified by many experiences besides its taste during the act of consumption.

A Disclaimer

(Those of you who have read Part VI have already seen this disclaimer, and can skip it.)

I’ve put off writing these next few articles because they’re likely to cause some controversy, which I don’t enjoy. My objective with the articles I write here at gnolls.org is to organize, distill, and summarize the bewildering variety of nutritional information into succinct, helpful articles, to share them with my readers, and to improve them as new information comes to my attention.

(An aside: I thank you, my readers, for continuing to provide references, intriguing leads, and constructive criticism. Please continue to do so.)

Please note that I have no horse in any of the current races: I am neither selling diet books nor defending a career-building hypothesis, and “Why Are We Hungry?” started long before the AHS and any still-simmering disputes.

Finally, and most importantly, I am not proposing any new theories of hunger or obesity. The current literature is both comprehensive and, I believe, more than adequate to explain and understand observed phenomena.

That being said: let’s get started!

Reward Is Fundamental And Necessary: We Have “Likes” And “Wants” For Very Important Reasons

Even the irreligious tend to take the theological viewpoint on hunger: the desires of the body are sinful, and exist to tempt us into gluttony and sloth. (See: doctrine of original sin.)

This type of thinking leads us astray. Our tastes are the product of millions of years of natural selection, during which animals that didn’t have our tastes died out and were replaced by those that did. They don’t exist to make us fat: they exist to keep us alive. As I’ve said in Part II, “Any animal whose faulty perceptions and motivations caused it to become obese, emaciated, malnourished, or poisoned by excess would have been strongly selected against.”

For example, we both “like” and “want” salt because all animals, including humans, require salt to live. Life never left the ocean: we carry it within us, in every cell.

Proceedings of the National Academy of Sciences, July 11, 2011
Relation of addiction genes to hypothalamic gene changes subserving genesis and gratification of a classic instinct, sodium appetite
Wolfgang B. Liedtke, Michael J. McKinley, Lesley L. Walker, Hao Zhang, Andreas R. Pfenning, John Drago, Sarah J. Hochendoner, Donald L. Hilton, Andrew J. Lawrence, Derek A. Denton

“Salt appetite and hedonic liking of salt taste have evolved over >100 million years (e.g., being present in Metatheria).
    …
An instinctive behavior pattern of which salt appetite is an exemplar reflects a genetically hard-wired neural organization naturally selected because of its high survival value.”

(Also see “The Salt-Mining Elephants of Kitum Cave”, from Part IV.)

And the fact that our taste for salt generally exceeds our needs can be explained by the fact that excess salt (within limits) is not harmful, whereas insufficient salt leads to death.

Among other interesting facts, Liedtke et.al. point out, somewhat breathlessly, that the desire for salt is mediated by the same brain circuits that mediate drug addiction. This is true—but those same brain circuits mediate all our motivations, from shelter to sex to social status. As I’ve said before, reward is not a concept limited to food. Reward is the reason we’re motivated to do anything at all.

To illustrate, here’s an actual graph of neural firing rates in the ventral pallidum, a hotspot of “liking” (hedonic reward). As we’d expect, rats liked intensely salty water when salt-deficient—even more than sugar water—and disliked it when previously fed a diet with sufficient salt.

Rat response to salt and sugar water

Amy J. Tindell, Kyle S. Smith, Susana Peciña, Kent C. Berridge and J. Wayne Aldridge
Ventral Pallidum Firing Codes Hedonic Reward: When a Bad Taste Turns Good
AJP – JN Physiol November 2006 vol. 96 no. 5 2399-2409

We compared VP neural firing activity in rats during aversive “disliking” reactions elicited by a noxiously intense NaCl taste (triple-seawater 1.5 M concentration) in normal homeostatic state versus in a physiological salt appetite state that made the same NaCl taste palatable and elicit positive “liking” reactions. We also compared firing elicited by palatable sucrose taste, which always elicited “liking” reactions in both states. A dramatic doubling in the amplitude of VP neural firing peaks to NaCl was caused by salt appetite that matched the affective switch from aversive (“disliking”) to positive hedonic (“liking”) reactions. By contrast, VP neural activity to “liked” sucrose taste was always high and never altered.

And again, we see that “wanting” and “liking” are not magical properties of food—they’re values we assign to food (and everything else) based on our past experience and nutritional state.

Why Do We Ever Stop Eating Delicious Food?

If incentive salience is the controlling factor of how much we eat, why do we ever stop eating? Why don’t we simply eat until we can’t move, repeat as soon as we’re able, and continue until we all require mobility scooters?

Oreo Cookies!!The answer cannot be in the food itself: the last Oreo in the package is no different than the first Oreo. “Palatability” is a value we assign to food, not an intrinsic property of the food itself, as I’ve already discussed here, in Part VI. Otherwise everyone in the world would “like” exactly the same foods.

I’ll repeat this, because it’s important: the Oreo didn’t change. We did.

Obviously there must be some drive within us that modulates incentive salience (“wanting”)—some motivation that causes us to stop eating before we vomit or physically burst. And many of my readers have already come to the correct conclusion: that drive is satiation, which I’ve already described at length here.

Note that satiety can also come into play if we’ve been eating for long enough. Though satiety and satiation are clearly defined, there is no bright line between them as they are experienced: the timing of the satiety response depends dramatically on what’s being eaten and how it’s prepared, and can overlap with the satiation response.

(For more information, or to refresh your memory, I discuss satiety in Part IV, and satiation in Part V.)

Also note that these drives can become dysfunctional, so there are a few unfortunate people who eat until they vomit and/or require mobility scooters. I’ll discuss this in future installments.

Therefore, in order to estimate how much of a food we are likely to consume, we must examine its power to produce satiation and satiety, as well as its incentive salience.

Modulation Of Reward Doesn’t Require Taste At All

Hedonic impact and incentive salience are modified by the entire set of circumstances around eating, not just taste. Here’s a startling study:

Ivan E. de Araujo, Albino J. Oliveira-Maia, Tatyana D. Sotnikova, Raul R. Gainetdinov, Marc G. Caron, Miguel A.L. Nicolelis, Sidney A. Simon
Food Reward in the Absence of Taste Receptor Signaling
Neuron Volume 57, Issue 6, 27 March 2008, Pages 930-941

Here we show that trpm5−/− mice, which lack the cellular machinery required for sweet taste transduction, can develop a robust preference for sucrose solutions based solely on caloric content. Sucrose intake induced dopamine release in the ventral striatum of these sweet-blind mice, a pattern usually associated with receipt of palatable rewards. Furthermore, single neurons in this same ventral striatal region showed increased sensitivity to caloric intake even in the absence of gustatory inputs.

Not only did the taste-blind rats develop a preference for sugar water over plain water—their preference was just as strong in all measurements as the mice with functional taste receptors!

(Clearly the satiety response can affect our reward responses, irrespective of taste.)

Satiation and Satiety: Putting The Brakes On Liking And Wanting

It is very important to recall here that satiation is an estimate of future satiety, based on sensory input.

“This finding of concerted gene regulation was attenuated on gratification with perplexingly rapid kinetics of only 10 min, anteceding significant absorption of salt from the gut.” -Liedtke et.al.

In other words, the satiation response is sufficient to stop salt consumption: we don’t have to wait for satiety (absorption from the gut) to tell us to stop ingesting salt.

As we’d expect, satiation and satiety cause a decrease in “wanting” as well as “liking”. And here’s another blockbuster:

Physiology & Behavior
Volume 98, Issue 3, 7 September 2009, Pages 318-325
Eating what you like induces a stronger decrease of ‘wanting’ to eat
Sofie G.T. Lemmens, Paul F.M. Schoffelen, Loek Wouters, Jurriaan M. Born, Mieke J.I. Martens, Femke Rutters and Margriet S. Westerterp-Plantenga

‘Liking’ and ‘wanting’ scores of all fasted subjects on the two test-days showed 62–73% reproducibility. CM [chocolate mousse] was liked more than CC [cottage cheese] (p < 0.001). Consumption of CM decreased ‘wanting’ for bread, filling, drinks and dessert (p < 0.03). Consumption of CC decreased ‘wanting’ for bread only (p < 0.05). Contrary to CC, CM decreased relative ‘liking’ for the dessert category (p < 0.001). In conclusion, the computer test for measurement of ‘liking’ and ‘wanting’ is sufficiently valid. Eating a highly liked food item induces a more distinct decrease in ‘wanting’ for food items in general and category-specific ‘liking’, than eating a sufficiently liked neutral food item.

Chocolate mousse induced a larger decrease in hunger and desire to eat than cottage cheese, although the offered amount of both food items was isoenergetic.

Lemmens et.al. demonstrates that eating delicious, highly “liked” food (food with high hedonic reward, aka “palatable” food) does not necessarily cause us to eat more. In fact, in their experiment, the subjects were less motivated to earn more food after eating the chocolate mousse than after the cottage cheese!

Given this data, it seems likely that eating the government-recommended low-salt, low-fat diet simply increases the hedonic impact of fat and salt—increasing the probability that we’ll consume it in the form of junk food instead of eggs, fatty meat, coconut milk, and other nutritious foods.

Intermission

Getting Tired Of Food: “Sensory-Specific Satiety”

Space does not permit a full discussion of sensory-specific satiety. To summarize quickly, it’s the effect by which both our “liking” and our “wanting” for a food decrease as we eat it, irrespective of its other characteristics. For example:

Appetite. 2009 Feb;52(1):222-5. Epub 2008 Oct 4.
Food liking, food wanting, and sensory-specific satiety.
Havermans RC, Janssen T, Giesen JC, Roefs A, Jansen A.

Participants had to consume a certain amount of chocolate milk and afterwards approximately half of the participants played a game to obtain more chocolate milk, whereas the other half played a game to obtain crisps. Participants showed a decline in subjective liking of taste and smell of the chocolate milk in comparison to crisps. Furthermore, they showed less motivation (i.e. wanting) to obtain more chocolate milk. It is concluded that sensory-specific satiety in humans reflects a decrease in both food liking and food wanting.

[Note that “satiety” is somewhat of a misnomer. Depending on the time between consumption and testing, the satiation response is often still in play—and since this effect is dependent on taste, I believe “sensory-specific satiation” is a more appropriate name. But “sensory-specific satiety” is the accepted scientific terminology, so I’ll continue to use it.]

In the vernacular, we call this “getting tired” of a food, as in “I don’t even want to LOOK at another guava right now.” This effect is very well-established, and points to the idea that variety may be a greater motivator of consumption than palatability. I may explore this issue in more detail if there is demand.

Palatability Affects Satiation But Not Satiety (That’s A Quote)

Even if we consume more food at a sitting, this does not automatically mean we’ll consume more calories throughout the day. A metabolically functional person who eats more food will simply be sated for longer, because hedonic reward doesn’t affect satiety:

Physiol Behav. 1999 Jun;66(4):681-8.
Palatability affects satiation but not satiety.
De Graaf C, De Jong LS, Lambers AC.

The results showed that the ad lib intakes of the less pleasant and unpleasant soups were about 65 and 40% of the intake of the pleasant soup. Subjects ingested about 20% more soup when the subjects had to wait for the test meal about 90 min, compared to the 15 min IMI condition. The availability of other foods had no effect on the effect of pleasantness on ad lib intake. There was also no effect of the pleasantness on subsequent satiety: hunger ratings and test meal intake were similar after the three standardized soups. One conclusion is that pleasantness of foods has an effect on satiation but not on subsequent satiety.

These are common-sense results: eating a palatable food doesn’t magically decrease its nutritive value. And given equal satiating power, we may eat more of the palatable food—but having eaten more, we’ll also experience greater satiety.

(Do note that tomato soup is extremely non-satiating under the best of circumstances: the standardized soups contained 350g for women and 500g for men. This translates to 105 and 150 kcal (“calories”), respectively, with essentially zero fat or protein, and of which the majority is sugar. In other words, nutritively, they’re candy plus a bit of starch and a few vitamins…and the reason anyone stops eating it is most likely due to the effect of sensory-specific satiety.)

Most importantly, we might eat less of unpalatable foods—but having eaten less, we’ll be more hungry afterward.

J Nutr. 2011 Mar;141(3):482-8. Epub 2011 Jan 26.
Staggered meal consumption facilitates appetite control without affecting postprandial energy intake.
Lemmens SG, Martens EA, Born JM, Martens MJ, Westerterp-Plantenga MS.

Participants (n = 38, age = 24 ± 6 y, BMI = 25.0 ± 3.1 kg/m(2)) came to the university twice for consumption of a 4-course lunch (40% of the daily energy requirements) in 0.5 h (nonstaggered) or in 2 h with 3 within-meal pauses (staggered) followed by ad libitum food intake.
    …
However, this [staggered meal consumption] was not translated into lower energy intake.

In other words, eating the same food over a longer period of time doesn’t cause anyone to eat any less…

…assuming we’ve eaten real food. Consuming junk food will always leave us hungry: candy has no satiating power, and will not produce satiety, no matter what circumstances we consume it under. (Recall again that satiation is an estimate of future satiety, and satiety is nutritionally driven.)

Wrapping Up: Just What Is Incentive Salience, Anyway?

We now know that hedonic reward (“liking”, “palatability”) does not alter a food’s power to produce satiety, because satiety is not modulated by taste. And though “sensory-specific satiety” (again, a partial misnomer: the satiation response is involved) is a well-understood phenomenon, reward’s power to affect incentive salience (“wanting”) depends strongly on circumstances and whose studies you believe.

In other words, to make any sense of the situation, incentive salience (“wanting”) must be understood as a product of hedonic impact (“liking”), satiation, and satiety—and the limit on our food consumption comes primarily from its satiating and sating power, not its hedonic impact (“palatability”).

This neatly solves the conundrum that some current theories of “food reward” face: they must claim that foods like bacon-wrapped filet mignon and pâté de foie gras lack the magical property of “food reward”, even though they’re delicious (in other words, “your food isn’t rewarding, it just tastes like it”)—and that foods like Wheat Thins and Pringles have this same magic property of “reward” in excess, even though they’re not nearly as delicious as that bacon-wrapped filet.

It also explains common observations like “There’s always room for dessert”…because dessert, being nutritionally incomplete, is not satiating.

Finally We Can Define “Hyperpalatability”

Previously the term “hyperpalatable” has been like “pornography”: we know it when we see it, but we can’t define it—or we define it circularly, as “tasty foods which we overeat”.

However, now that we understand that how much we eat is determined by the opposing forces of satiation, satiety, and incentive salience (“wanting”), we can easily understand why certain foods are hyperpalatable: they combine a meaningful amount of hedonic reward with an inability to produce satiation or satiety, resulting in incentive salience that doesn’t decrease as you eat.

To draw an analogy: hedonic impact (“liking”) is the gas pedal, satiation (and, after a delay, satiety) are the brakes, and the speed of the car is incentive salience (“wanting”). We can eat foods with high hedonic impact—but so long as they also produce satiation (and, eventually, satiety), the car will stop. However, if we eat foods that do not satiate (or sate), our car has no brakes, and it won’t stop no matter how slowly it’s moving.

And now we can see why hyperpalatable foods don’t necessarily taste as good as your favorite foods: they don’t have to! All they have to do is be made of ingredients so nutritionally empty that they never produce satiation or satiety (e.g. linoleic acid and fructose), and be so calorie-dense that they don’t fill up our stomachs until we’ve eaten pathological amounts.

This leads us to a disturbing conclusion: the worse a snack food is for us, the more difficult it usually is to stop eating. Read my article “Why Snack Food Is Addictive: The Grand Unified Theory of Snack Appeal” for a deeper exploration of this subject.

Conclusion: It’s Not Just The Taste, It’s The Nutrition (And Much More)

If we find ourselves overeating a food, we need to ask ourselves “Is this a nutritious, whole food, containing complete protein, healthy fats, and a generous helping of nutrients?” For most of us, the answer will be “No, it’s Corn Pops,” or some other nutritionally incomplete junk.

No carbs != healthy.Just because a snack doesn’t contain carbohydrates or HFCS doesn’t mean it’s not junk food. Nuts, for instance, generally contain incomplete protein and large quantities of omega-6 PUFA (linoleic acid)…cake made with xylitol and nut flour is still cake, not food. Fruit is good in moderation, but in excess (especially as juice) it’s just sugar with some vitamins. And snacking is bad for many reasons, even if you’re eating “healthy” snacks.

  • Reward systems drive all our behaviors, not just our food preferences.
  • Liking and wanting don’t exist just to make us fat: they exist to keep us alive. They are the product of millions of years of natural selection, during which animals that didn’t have our tastes died out and were replaced by those that did.
  • Liking and wanting are values we assign to food, not invariant or intrinsic properties of the food itself.
  • The modulation of reward (liking and wanting) does not require taste at all.
  • Incentive salience (“wanting”) is a product of hedonic reward (“liking”), satiation, and satiety.
  • Eating food you like may either decrease or increase your want for more, depending on the food, the circumstances, and whose studies you believe.
  • Palatability can affect satiation, either via nutritional satiation or “sensory-specific satiety”, but it does not affect satiety.
  • Hyperpalatability is an unnatural amount of hedonic reward, combined with an inability to produce satiation or satiety. Therefore, the worse a snack food is for you, the more difficult it usually is to stop eating.
  • Conclusion: in order to keep incentive salience (“wanting”) under control, make sure that hedonic impact (“liking”) is always accompanied by nutrition. Eat delicious but nutritionally dense foods, containing complete protein, healthy fats, and ample nutrients. Otherwise you’re eating food with no brakes.
  • And when you do take the risk, eat your cheat food after you’ve already satiated yourself with a complete meal.

Continue to Part VIII, “It’s Just Like Drug Addiction EVERYONE FREAK OUT: The Role And Limits Of Reward”

Live in freedom, live in beauty.

JS


(This is part VII of a series. Go back to Part I, Part II, Part III, Part IV, Part V, or Part VI.)

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Hedonic Impact (“Liking”), Incentive Salience (“Wanting”), and “Food Reward”: Why Are We Hungry? Part VI

Caution: contains SCIENCE!

Now we enter the heretofore-murky waters of liking, wanting, and “food reward”.

(Part VI of a series. Go back to Part I, Part II, Part III, Part IV, or Part V—or go on to Part VII.)

Summary: The Story Thus Far

In previous installments, we’ve established the following:

  • Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.
  • In a properly functioning human animal, likes and wants coincide; satiation is an accurate predictor of satiety; and the combination of hunger signals (likes and wants) and satisfaction signals (satiation and satiety) results in energy and nutrient balance at a healthy weight and body composition.
  • Restrained eating requires the exercise of willpower to override likes, wants, and the lack of satiation or satiety; the exercise of willpower uses energy and causes stress; and stress makes you eat more. Therefore, a successful diet must minimize the role of willpower.
  • A lack of satiety will leave us hungry no matter what else we do to compensate. We fail to achieve satiety by not ingesting (or not absorbing) the energy and/or nutrients our body requires, and by an inability to retrieve the energy and/or nutrients our bodies have stored due to mitochondrial dysfunction.
  • Satiation is an estimate of future satiety based on sensory input. As with satiety, we fail to achieve it by not satisfying our nutritional needs. We can also bypass satiation by decreasing sensory exposure to our foods. Some common enablers are eating quickly, eating while distracted or on the run, and eating calorie-dense packaged and prepared foods.

A Disclaimer

I’ve put off writing these next few articles because they’re likely to cause some controversy, which I don’t enjoy. My objective with the articles I write here at gnolls.org is to organize, distill, and summarize the bewildering variety of nutritional information into succinct, helpful articles, to share them with my readers, and to improve them as new information comes to my attention.

(An aside: I thank you, my readers, for continuing to provide references, intriguing leads, and constructive criticism. Please continue to do so.)

Please note that I have no horse in any of the current races: I am neither selling diet books nor defending a career-building hypothesis, and my current series of articles started long before the AHS and any still-simmering disputes.

Finally, and most importantly, I am not proposing any new theories of hunger or obesity. The current literature is both comprehensive and, I believe, more than adequate to explain and understand observed phenomena.

That being said: let’s get started!

Endless Arguments Are Often A Sign Of Murky Definitions

When, after innumerable posts and presentations on the subject, we see very smart people unable to articulate exactly what is meant by fundamental concepts like “palatability”, it’s quite likely that the hypothesis in question is poorly specified.

Therefore, I will briefly summarize the current state of scientific knowledge, as I understand it, on the subject of hunger and reward.

Defining Our Terms: “Liking” = Hedonic Impact, “Wanting” = Incentive Salience

Though the terms “liking” and “wanting” seem reasonably self-explanatory, we must be careful when using them in the scientific sense.

When we speak of “liking” something, we’re consciously predicting our future reactions. (“I like eggs.”) However, in the scientific literature, “liking” refers only to our actual reactions of pleasure, both conscious and unconscious—the hedonic impact of an experience.

Similarly, when we speak of “wanting”, we’re consciously predicting our future likelihood of seeking out an experience. But again, in the scientific literature, “wanting” refers only to our actual motivation to do so—the incentive salience of an experience.

Curr Opin Pharmacol. 2009 Feb;9(1):65-73. Epub 2009 Jan 21.
Dissecting components of reward: ‘liking’, ‘wanting’, and learning.
Berridge KC, Robinson TE, Aldridge JW.
[Note: free full text]

In recent years significant progress has been made delineating the psychological components of reward and their underlying neural mechanisms. Here we briefly highlight findings on three dissociable psychological components of reward: ‘liking’ (hedonic impact), ‘wanting’ (incentive salience), and learning (predictive associations and cognitions).

The concept of “palatability” can be understood as the hedonic reward of food:

For most people a ‘reward’ is something desired because it produces a conscious experience of pleasure — and thus the term may be used to refer to the psychological and neurobiological events that produce subjective pleasure. But evidence suggests that subjective pleasure is but one component of reward, and that rewards may influence behavior even in the absence of being consciously aware of them. Indeed, introspection can actually sometimes lead to confusion about the extent to which rewards are liked, whereas immediate reactions may be more accurate [1]. In the extreme, even unconscious or implicit ‘liking’ reactions to hedonic stimuli can be measured in behavior or physiology without conscious feelings of pleasure (e.g. after a subliminally brief display of a happy facial expression or a very low dose of intravenous cocaine) [2,3].
-Ibid.

And when most of us think of “food reward”, we are thinking purely of “wanting”—specifically “incentive salience”:

By ‘wanting’, we mean incentive salience, a type of incentive motivation that promotes approach toward and consumption of rewards, and which has distinct psychological and neurobiological features. For example, incentive salience is distinguishable from more cognitive forms of desire meant by the ordinary word, wanting, that involve declarative goals or explicit expectations of future outcomes, and which are largely mediated by cortical circuits [34–37].

By comparison, incentive salience is mediated by more subcortically weighted neural systems that include mesolimbic dopamine projections, does not require elaborate cognitive expectations and is focused more directly on reward-related stimuli [34,35,38]. In cases such as addiction, involving incentive-sensitization, the difference between incentive salience and more cognitive desires can sometimes lead to what could be called irrational ‘wanting’: that is, a ‘want’ for what is not cognitively wanted, caused by excessive incentive salience [39•,40•,41]. [emphasis mine]
-Ibid.

That explains quite a bit right there, doesn’t it?

I’d love to quote more of Berridge et.al.—but as the full text is available for free, I’ll just recommend that you read it if you’re interested in digging into the details.

It should now be clear that “food reward” has three distinct components which we must distinguish and define if we hope to understand it:

  • The hedonic impact of eating food: its palatability.
  • Incentive salience: the drive to consume more food.
  • The process of learning, in which both hedonic impact and incentive salience are modified by experience.

If we fail to separate these components, we find ourselves creating tautologies. For example, it’s obviously absurd to say alcoholism is caused by “alcohol reward”—but if we distinguish the hedonic impact of alcohol from the incentive salience of alcohol, suddenly we have a handle by which to grasp the issues and make headway.

Intermission

Some Important Observations About Liking, Wanting, and Learning

Here are what I believe are some important takeaways from the literature as they apply to hunger:

  • Reward is not a concept limited to food. Common sources of reward in everyday life also include social approval from parents, friends, co-workers, and strangers; legal and illegal drugs; physical activities, such as recreational sports; successful accomplishment of tasks; and media consumption, including television and the Internet. Anything we “like”—anything with hedonic impact—is capable of creating and reinforcing a “want” for more—incentive salience.
        In fact, much of the literature studies drug reward (legal and illegal). These are easier cases to study, since the human body has no nutritional requirement for nicotine, alcohol, or cocaine, and reward is not tied up with other motivations.
  • Taste is not the only determinant of hedonic impact. The circumstances surrounding consumption, such as social approval, are also powerful determinants…and they don’t even have to be associated with consumption!
        For example, beer is generally an acquired taste: most of us instinctively dislike its bitterness, and only ‘develop a taste’ for beer as we associate beer drinking with intoxication and positive social interactions. Note the universal context of beer commercials: beer = fun times with friends. Also note that advertising can drive consumption, despite having no association with the actual action of consumption.
        Another example: many Muslims and Jews are repulsed by even the thought of pork purely due to social context, despite having no intrinsic inability to ingest or digest it.
  • Incentive salience (“wanting”) is not an intrinsic property of food, or anything else. Unlike our instinctive aversion to spiders, humans have no instinctual knowledge of Pringles, Twizzlers, or Cinnabons. Incentive salience is a learned property.
  • Therefore, incentive salience (“wanting”) is not a static property. It is created and reinforced by the hedonic impact (“liking”) of food consumption itself, by the positive experiences of satiation and satiety that consumption of nutritious food can produce, and by its associations with other rewarding factors and experiences (as enumerated above).
  • We must distinguish experiences that modify hedonic impact (“liking”) or incentive salience (“wanting”) from incentive salience itself. For instance, the fact that the satiety response can modify incentive salience does not make satiety part of the reward response.
        It’s even easier to understand this error when we understand that social context affects hedonic impact: it’s clearly silly to call social relationships part of “food reward”. This error has been a major source of confusion in the discussion so far.

Conclusion

In order to understand the role of “food reward” in hunger, we must define and distinguish its constituent motivations:

  • The hedonic impact of eating food: its palatability.
  • Incentive salience: the drive to consume more food.
  • The process of learning, in which both hedonic impact and incentive salience are modified by experience.

Further, we must understand that reward is not limited to food, is neither static nor an intrinsic property of the food itself, and is modified by many experiences besides its taste during the act of consumption—most of which are not themselves reward pathways.

We’ll start exploring these motivations and interactions—and how they fail—in Part VII. Click here to keep reading!

Live in freedom, live in beauty.

JS

(Part VI of a series. Go back to Part I, Part II, Part III, Part IV, or Part V—or go on to Part VII.)


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Why Are We Hungry? Part II: Hunger Is The Product Of Multiple Perceptions And Motivations, Sometimes Conflicting

Caution: contains SCIENCE!

Part I of this series clearly establishes the following, which I hope is non-controversial:

Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.

This is intuitively obvious to everyone: hunger is not a generic drive, satisfiable by shoving a generic substance called “food” into our mouths. The fantasy of “food pills” remains squarely in the Future That Never Was, along with flying cars and nuclear power too cheap to meter.

City of the Future

I miss the future that never was.

While a bewildering variety of “meal replacement drinks” exists, walking down any commercial street in the world reveals restaurants—not kiosks with a row of Slurpee machines filled with flavors of Ensure, Slim-Fast, and Muscle Milk. And even the most dispiriting accretion of fast-food dispensaries around a freeway exit features everything from hamburgers to burritos to chicken salads to tuna sandwiches.

Fortunately, it’s possible to cut through the fog of conflicting motivations by analyzing these four drives in detail: “liking” and “wanting”, which make us eat, and “satiation” and “satiety”, which make us stop eating.

First, let’s define the four drives. I’ll start with the end of the process, for reasons that will become clear.

What Is Satiety? What Does “Sated” Mean?

“Satiety” is our body’s response to the absorption of nutrients through the intestine.

Nutrition Bulletin Volume 34, Issue 2, pages 126–173, June 2009
Satiation, satiety and their effects on eating behaviour
B. Benelam

When nutrients reach the intestine and are absorbed, a number of hormonal signals that are again integrated in the brain to induce satiety are released.

The important takeaway here is twofold. First, satiety is not a conscious response over which we have any control. Satiety is our body’s direct measurement of actual nutrient intake—a system honed over hundreds of millions of years of evolution. It answers the question “Should I seek out food now—or can I do something else, like seek a mate, play with my children, or take a nap?”

Second, since satiety is based on actual nutrient absorption, which occurs through the small intestine, it takes a long time to receive any satiety cues from the food we eat. As I describe in this article, it takes 2.5-3 hours before half of a mixed meal has even left the stomach, much less been absorbed through the intestine! GI transit times vary dramatically, and are shorter for highly processed, fat-free foods—but it’s clear that satiety takes far too long for it to be a useful signal to stop eating.

Most likely this is why satiation is a separate biochemical process.

What Is Satiation? What Does “Satiated” Mean?

Satiation occurs when the value we place on another bite of food drops below zero. It is our estimate of the marginal utility of eating the next piece of food.

For those not familiar with the economic term, “marginal utility” refers to the value we place on acquiring one more of something. “Marginal” means that we may already have some of it, i.e. we may not be starting from zero. Furthermore, the concept of “diminishing marginal utility” is often useful, because the value we place on something usually decreases as we accumulate more of it. (There are exceptions, which we’ll discuss later.)

This is easy to demonstrate: imagine that we’re at a big outdoor concert, like Coachella. It’s very hot outside, we’re thirsty from standing in the sun and shouting along to bands we like, it would take us a long time to get out to the car and back in, and we don’t want to miss the next band. A cold bottle of water might be worth $5 to us at that point, or even more…so we willingly pay the extortionate $4 from the kiosk. Once we drink it, though, we’re no longer as thirsty as we were, so the value we place on a second bottle might be only $2. However, since the venue still charges $4, we don’t buy a second bottle. In other words, a transaction only occurs if the value we place on something is greater than or equal to the price at which it’s available.

It’s easy to understand satiation by going to an all-you-can-eat buffet: the value we place on each additional plate of food decreases until we decide it’s not even worth getting up from the table to take more—though we could have it for free!

Satiation is not the same thing as being full, or being sated. If all we have in the house is a jar of sweet pickles and a bag of Twizzlers, we might quickly become satiated, since we don’t want to eat any more of either. However, this does not leave us sated: our body knows that pickles and Twizzlers do not contain the nutrients we need to live.

The important distinction here is that satiation is an estimate, based on the sensory experience of eating. Ideally, satiation would accurately predict future satiety—but while satiety is a direct measurement of nutrient intake, and cannot be easily fooled, satiation is dependent on our perceptions.

You Can Fake Satiation, But You Can’t Fake Satiety

Satiation is affected by our senses of taste, smell, texture, and stomach distention; it’s affected by our perception of a food’s caloric and nutritional value; and it’s even affected by mundane considerations like serving size. Not only can satiation be overridden by sufficiently powerful wants, our perceptions of satiation (= future satiety) can easily be influenced or fooled entirely.

Signals about the ingestion of energy feed into specific areas of the brain that are involved in the regulation of energy intake, in response to the sensory and cognitive perceptions of the food or drink consumed, and distension of the stomach. -Ibid.

Many different experiments prove that satiation can be manipulated: here are a couple I found interesting. Let me know if you find others!

J. Nutr. February 2009 vol. 139 no. 2 394-399
Hidden Fat Facilitates Passive Overconsumption
Mirre Viskaal-van Dongen, Cees de Graaf, Els Siebelink, and Frans J. Kok

“In the presence of visible fats, energy intake was lower than in the presence of hidden fats, suggesting that hidden fats may contribute to overconsumption.”

The effect was minor but significant: 8-9%. Our perceptions do not perfectly estimate the nutritive content of foods.

Am J Clin Nutr August 2009 vol. 90 no. 2 269-275
Effect of bite size and oral processing time of a semisolid food on satiation
Nicolien Zijlstra, René de Wijk, Monica Mars, Annette Stafleu, and Cees de Graaf

“Conclusion: This study shows that greater oral sensory exposure to a product, by eating with small bite sizes rather than with large bite sizes and increasing OPT [oral processing time], significantly decreases food intake.”

The effect was striking: people ate up to 50% more when able to eat freely vs. when limited to small bites every nine seconds! Therefore, satiation is also affected by how fast we eat and how big of a bite we take. The old advice to “eat slowly and mindfully” and “take small bites” does have some scientific support.

The study also contains this hidden gem: “The subjects had to be healthy, be aged 18–30 y, be of normal weight [body mass index (in kg/m2): 18.5–25.0], and like chocolate custard.”

What Is “Liking”? What Are “Likes”?

Psychopharmacology doi:10.1007/s00213-008-1099-6
Affective neuroscience of pleasure: reward in humans and animals
Kent C. Berridge and Morten L. Kringelbach

Liking: the actual pleasure component or hedonic impact of a reward. Pleasure comprises two levels: (1) core ‘liking’ reactions that need not necessarily be conscious; (2) conscious experiences of pleasure…

In common usage, “liking” is the reward we anticipate from future consumption. However, in scientific usage, “liking” refers to the pleasure we feel from actually eating food—its hedonic impact.

Like “satiation”, “liking” is situationally dependent, and it is only nominally under conscious control. Cultural and social conditioning can affect our likes, particularly as children: for instance, most non-Japanese people find natto disgusting, and most non-Filipinos have a difficult time with balut.

BLEEEEAAAAARGH

It reminds me of Giger's "Alien".

Yes, that's a chicken embryo.


And though we cannot simply choose to “like” something, conscious efforts to affect our preferences will sometimes have an effect over time: for instance, most children find beer disgusting, and it’s well-known that most of us must “develop a taste” for it.

It is important to note that palatability is a major component of “liking”, and “hedonic impact” is the technical term for the pleasure associated with actual consumption. However, we must be careful to distinguish the reward itself from our perception of it. When we say we “like” a food, we may also be taking conscious perceptions and biases into account.

Neurosci Biobehav Rev 20(1) 1-25, 1996.
Food reward: Brain substrates of wanting and liking
KC Berridge

Food reward is not simply a physical property of a taste stimulus itself…Palatability, or the hedonic component of food reward, instead results from a central integrative process that can incorporate aspects not only of the taste, but of the physiological state and the individual’s associative history.

What is “Wanting”? What Are “Wants”?

“Wanting: motivation for reward, which includes both (1) incentive salience ‘wanting’ processes that are not necessarily conscious and (2) conscious desires for incentives or cognitive goals.” -Berridge and Kringelbach

Rephrased: Wants are desires at a specific moment in time. We measure them by how motivated we are to actually go out and get whatever it is we ‘want’. Applied to food, we often use the word “appetite”.

Note that wants are partially, but not entirely, under our conscious control. I might know that cake is bad for me, but that doesn’t stop me from wanting cake. Furthermore, wants vary dramatically over time depending on the degree of satiation and satiety we are experiencing. To use my previous example, if I’ve just eaten a 20-ounce prime rib, I’m unlikely to want any more prime rib…but that doesn’t mean I like prime rib any less.

You’ll note that I’m carefully avoiding the gory biochemical details of these sensory and motivational pathways. This is intentional, and it’s for two reasons: first, we don’t completely understand them, and second, they don’t really matter. The details of ghrelin, leptin, cholecystokinin, peptide YY, and the dopamine-reward system are fascinating…but since we’ve already demonstrated that there’s no magic pill we can take that blunts our hunger without making us poop our pants, we don’t have to understand all of the details.

In short, we can understand wanting, liking, satiation, and satiety (and their interactions) on a purely functional level. We don’t have to understand the biochemistry of these drives in order to eat like a predator.

However, if you want to dive in, I recommend turning to chapter 7.3 of the online textbook Endotext, “The Regulation of Food Intake in Humans”. Its authors include several co-authors of papers I’ve cited in this series.

We can relate satiation and wanting in this common-sense way: satiation occurs when we don’t want any more food.

A Summary Of The Components Of Hunger

  • Likes (scientific usage) = the pleasures we experience from eating, known scientifically as “hedonic impact”.
  • Wants = desires at a specific moment. A measure of our motivation to attain a reward. Our “appetite”.
  • Satiation = absence of motivation to eat more. The absence of attainable wants. An estimate of future satiety, based on the sensory experience of eating.
  • Satiety = a signal from your body that it is replete with nutrients.

Perceptions And Motivations In Harmony And In Conflict:
Evolutionary Concordance And Discordance

Ideally, if everything were functioning properly, our likes and wants would always coincide, satiation would always be an accurate predictor of satiety, and the combination of hunger signals (likes and wants) and satisfaction signals (satiation and satiety) would result in energy and nutrient balance.

Existing in this state of harmony and balance would have been strongly selected for throughout tens of millions of years of evolutionary history, all the way back to the great apes and beyond. Any animal whose faulty perceptions and motivations caused it to become obese, emaciated, malnourished, or poisoned by excess would have been strongly selected against.

However, we can see that both the simple states of hunger and non-hunger, in which our motivations agree, are just two possible outcomes of the collision of these four processes—and that just as hunger isn’t necessary to make us eat, non-hunger isn’t sufficient to make us stop eating.

Furthermore, we can see that these disorderly outcomes are most likely the product of evolutionary discordance.

I’ll explore some of those issues in Part III and beyond.

Live in freedom, live in beauty.

JS

Continue to Part III, “Willpower And Why It Fails.” (Or back to Part 1.)


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